=Entorachis) Anomocarellius Anomocarina Anomocarioides Anomocariopsis Anopocodia Anopolenus Anoria Antagmella Antagmopleura (=Poljakovia) Antagmus Antatlasia Anthracopeltis Anujaspis Anuloides
Ao Aocaspis Aotiaspis
Ap Apachia (=Apachilites) Apatokephalina Apatokephaloides Apatokephalops (=Aristokainella; =Wanliangtingia) Apatokephalus Apatolichas Aphelaspidella Aphelaspis (=Proaulacopleura; =Clevelandella; =Labiostria) Apheloides Aphelotoxon (=Ponumia) Apianurus Apiflabellum Aplexura Apocalymene Apollonaspis Apomodocia Apoplanias Appendicysta Aprathia
Ar Araeocephalus Aragotus Araiocaris Araiopleura Arapahoia (=Hesperaspis) Arator Arcadiaspis Archaeagnostus Archaeaspis Archaeocoryphe Archaeopleura Archaeuloma Archegonus (=Cylindraspis) Archikainella Arcifimbria Arcticalymene Arcticeraurinella Arctinurus (=Oncholichas; =Platynotus; =Pterolichas) Arctipeltis Arcuolenellus Arcuolimbus Arduennella Arduennops Areia Areiaspis Arellanella Argasalina Argentopyge Arglina Argunaspis Ariaspis Armagnostus Armorigreenops Arraphus Arrhenaspis Arthricocephalus (=Arthricocephalites; =Protoryctocara; =Oryctocarella) Arthrorhachis (=Metagnostus; =Girvanagnostus) Artokephalus